1. Field of the Invention
The invention relates to an apparatus for projecting an image onto the retina of a viewer's eye thereby allowing the viewer to perceive the image.
2. Description of the Related Art
There have been recently presented various types of image display apparatuses each projecting an image by scanning a light beam on the retina of a viewer's eye to thereby allow the viewer to perceive the image, which are each called, “Retinal Scanning Display.”
For example, Japanese Patent Publication No. HEI 11-142763 discloses a conventional image display apparatus including a scanning optical device scanning laser light in two-dimension; and optics (an optical device for light convergence) causing the laser light scanned by the scanning optical device to converge at a point in a viewer's eyeball.
The above conventional image display apparatus employs as the aforementioned optics, a semi-transparent mirror having its reflective surface formed as a portion of an ellipsoidal surface of revolution, which is a concave curved surface. Owing to the nature of the ellipsoidal surface of revolution having its two foci, a light beam, upon entry from one of the two foci into a point on the ellipsoidal surface of revolution, enters the other focus without exception.
In light of the above fact, the above conventional image display apparatus is configured such that one of the two foci of the ellipsoidal surface of revolution is coincident in position with a reflection point at which the laser light is reflected off the aforementioned scanning optical device, while the other focus is coincident in position with a convergence point at which the laser light is converged by the aforementioned optics within viewer's eyeball, thereby securing the laser light scanned by the scanning optical device to converge within the viewer's eyeball.